Automatic font color with gradient participant background creates UnsupportedOperationException

[jonasehrlich]

To Reproduce
Using skinparam ParticipantFontColor automatic while using any kind of gradient background for participants creates an UnsupportedOperationException.

Create the following diagram and compile it (plantuml-server)

@startuml
skinparam ParticipantFontColor automatic
participant bob #green|blue
@enduml

The output image contains a Java traceback caused by an UnsupportedOperationException.

Expected behavior

Proper selection of a correct automatic font color, or a failure during image generation.

Screenshots

Desktop:

• OS: macOS 13.3.1
• Browser: Chrome
• Version: 112.0.5615.49
• plantuml / graphviz version:

$ plantuml -version
PlantUML version 1.2023.3 (Thu Mar 09 18:30:18 CET 2023)
(GPL source distribution)
Java Runtime: OpenJDK Runtime Environment
JVM: OpenJDK 64-Bit Server VM
Default Encoding: UTF-8
Language: en
Country: US

PLANTUML_LIMIT_SIZE: 4096

Dot version: dot - graphviz version 7.1.0 (20230121.1956)
Installation seems OK. File generation OK

[arnaudroques]

Many thanks for the report.
This should be fixed now.